Titanium oxide production



Patented Nov. 16, 1942 TITANIUM 0E YRQDUCTEQN John Lewis Keats and Henry lvloroni Stark, Wilmington, Del, asslgnors to E. I. du Pont de Nc= mo & Copany, W gton, libel, a corporation of Delaware No Drawing. Application July 6, 1939,

do No. 283,953 4 son This invention relates to the production of titanium oxide, and more particularly to a process for accelerating the hydrolysis of titanium salt solutions used in the manufacture of pigmentuseful titanium oxide.

More specifically, the invention relates to a process for accelerating the hydrolysis of such titanium salt solutions, and particularly titanium -auli'ate. under conditions which are highly con- 'ducive for efiecting conversion of the hydrolysis precipitate to rutile crystalline state and at calculation temperatures 01 relatively low order.

Titanium oxide pigments are produced from titanium salt solutions (the sulfate, chloride,

etc.) by many well-known processes. Uselof ti- --tanium sulfate solutions in such production is production of a substanti rutile crystalline titanium oxide pigment, the individual particles of which are characteristically uniform and relatively minute in size, which pigment will desirably exhibit the highest potential hi power and be of requisite cercial high strength d color. A further specific object is to provide an improved process for the production of rutile titanium oxide from titanium salt solutions, and

particularly titanium sulfate, through use of an improved and novel type oi nucleating agent. An additional object of the invention is to provide a process for hydrol titanium salt 50*,

lutions, and particularly titanium sulfate, under such conditions that high yields of titanium ox ide are obtained. A further object is to clot a hydrolysis precipitate adapted to convert the anatase to the rutlle crystalline modification at comparatively low calcining temperatures.

These and other objects are attainable in this invention which comprises seeding a hydrolyzahle titanium salt solution with a spec and highly eflective nucleating agent, comprising suitably conditioned stannic oxide. 7

The novel nucleating sol of this invention possesses many distg features overprior of titanium chloride (upon observance of certain carefully chosen conditions) hydrolyze to produce rutile. 0f the three occurring crystalline modifications of titanium oxide, rutile possesses the highest refractive index and therefore the highest potential hidingpower. This high hiding power only exists, however, when the individual particles of the titanium oxide pigment are relatively uniform and minute in character, and,

preferably, smaller than exhibited by pigment anatase having certain optimum hiding power values. In such prior rutile pigment production, resort to calcination temperatures of a relative- 1y high order, 1. e., of substantially 1000 C. or higher, has been considered essential, and this even though use of such temperatures exerts an undesired degradation of and sacrifice in the strength and color of the final product.

We have found that arr excellent, high quality rutile titanium oxide pigment of relatively small and uniform particle size can be obtained in increased yields irom titanium salt solutions, and particularly titanium sulfate, through use or a nucleating agents, not only iii-respect to physical properties, but in seeding activity as well. it

comprises a more or less dilute, oolloidallydispersed, peptized hydrous stc oxide suspen sion. Peptization thereoi is preferably eiiected through suitably conditioning precipitated stem nic hydrate by treating the same with an acidic agent, such as hydrochloric acid. In describing? the invention, illustration will be given of one preferred embodiment in which hydrolysis is at iected of a titanium sulfate solution in the presence of peptlzed stannlc oxide as a nucleator with novel type of hydrolysis accelerating agent and celcination temperatures of a relatively lovc or der, 1. e., substantially below 1000 C.

In accordance with the invention, therefore,

hydrochloric acid as a peptizator:

In such preferred adaptation, a nucleating seed, peptized hydrous tin oxide, is prepared by precipitating stannic hydrate from an aqueous solution oi stc chloride by neutralimng said solution with sodium hydroxide (or other solution such as potassium or o ium laydroxide, carbonate, etc.) fllhe resultant stannic hydroxide precipitate is then filtered, washed thoroughly to remove all chloride ions present,

and, in purified state, a.ed with sutdciont hydrochloric acid as will provide a slurry mass at about 0.5 N. Such acid suspension is then preferably heated to an elevated 1 "1:1 rature (or substantially 50 0. or higher) and there main tained for a relatively. short period of (iii it is among it specific objects to provide for the '55 to 20 minutes) to suitabhv ction the drate and develop desired nucleating properties. The peptized seed suspension is then cooled, preferably quickly, to room temperature or lower, after which the same may be immediately used or stored, as desired, for subsequent use. 5

The amount of seed material required for effecting nucleation of the titanium sulfate solution will be found to be relatively small or minor.- An effectively useful amount comprises a quantity equal to about 3-5% (as $1102) on the basis of the T102 present, this amount being conveniently mixed with the solution prior to hydrolysis. Hydrolysis can then be effected in the usual and conventional manner.

By. use of our novel type of nucleating seed,

it will be found a materially increased yield of precipitated titanium oxide from the hydrolysis results within a relatively shorter period of time. Thus, a yield in excess of substantially 75 or 85% oi resmts after a period of three hours of go hydrolysis, whereas, in a comparable hydrolysis, but with an unseeded solution, a yield not to exceed so or 40% obtains. Again, when the anatase precipitate from such titanium sulfate hydrolysis is subjected to calcination, it will be sulfate or carbonate, and particularly potassium sulfate, a most useful agent, known to strongly inhibit rutile formation. Thus, conversion of an anatase precipitate to rutile is eflected without recourse to relatively high calcination temperatures whichwould otherwise undesirably afieet 40.

the pigment properties and diminish particularly the strength and color values of the final product.

' To a more complete understanding of the invention, the following specific examples are given. These, however, are merely illustrative and not in limitation of the invention:

' Baptized hydrous stannic oxide was prepared as follows: (8110145320) was dissolved in water and neutralized by running the solution into a solution of sodiim hydroxide (1.5 normal) until the pH-of the resulting suspension was 4.3. The precipitat ed stannic hydroxide was filtered and washed 5 to remove chloride ions and was then reslurried with water. A solution of HCl of 1.0 normal concentration was added to the slurry in an amount sufficient to make the HCl concentration of the resulting suspension 0.5 normal. The acid stances: I

Seeding hydrolysis and rawpiymeht with 8110s '4 I v 232 grams stannic chloride so suspension was then heated to and quickly cooled to room temperature.

1100 cc. of peptized stannic hydrate suspension prepared as above described was added to 2200 cc. of a solution of titanium sulfate. The SnOz equivalent of the stannic hydrate was equal to 5% of the T101. The concentration of the titanium sulfate solution after addition 01' the stannic hydrate suspension was 183 grams T10: per liter, 61.5 grams iron per liter, and 556 grams H2804 per liter. The seeded solution was heated at a temperature of 105 for a period of three hours. At the end of the hydrolysis 88% of the T10: originally present in the solution was found in the precipitate.

The raw pigment thus produced was char acterized by the tendency to convert to the rutile crystal form at relatively low calcining temperatures. Thus, it converted completely to rutile at 850 and was 60% rutile after calcining at 750. The conversion to rutile was complete after calcining at 850 even when the raw pigment was treated with potassium sulfate.

' Exmm II 370 a. SnCh.5H:O was dissolved in water and the solution neutralized to a pH of 6.2 by the addition of 2760 cc. of 1.5 N. NaOH. The stannic hydrate precipitate was washed and then peptized by adding HCl. This batch of seed was given no heat treatment.

The peptized stannic hydrate was added to the titanium sulfate solution before the beginning of hydrolysis. The amount of stannic hydrate added was equal to 5% as SnOz on the T102 basis. The composition of the solution during hydrolysis was =l83 grams per liter Fe =6l.5 grams per liter total H2SO4=556 grams per liter The yield on hydrolysis (3 hrs. boiling) 77.8%. Ufnseeded solutions yield about 30-40% when boiled the same period of 3 hrs.

The raw pigment from the above procedure converted to rattle completely on calcination at 850 C. and was found to be 60% converted after i calcination at 750 (3.

feature of lowering the temperature required for conversion of the raw pigment to rutile will be found to more advantageously accrue, and in the optimum, when said peptized stannic oxide is employed during hydrolysis of the titanium solution rather than subsequently thereto, as by adding said stannic oxide to a raw precipitated pigment prior to calcination. The ensuing data illustrate the comparative results in such in Crystal form of product sitar calolnatlon at- Sood addition 750 sec 050 1000 'i not tired stannic oxide (5 added to titanium mtiie Rutile. all? solution before new? 60% Beg; dgition NO as (1) raw pigment treated with Battle-Minam- 6- a Edlpepilzed stannic oxide (5%) added to wet row imam pgmou (4) %a%( s osd1fiem trta cofi e mu 10% trlflfle, Rama,

IE1! S0. (5) Contra yflrolysis roduct from U. 8. Reissue Pat. A l Mmw 518, seeding proc dure. No salt treatment. 3,, m

asomis oi suchagent in the same proportion to the titanium sulfate solution prior to hydrolysis.

While specific methods, agents and conditions have been employed in the specific examples above, obviously the invention is not limited thereto, such examples merely representing certain preferred and specific adaptations of the invention. Thus, while the preferred condition medium iorth'e stannic hydrate,hydrochloric acid, has been employed at specific concentrations, these are variable and use of acid concentrations ranging within, say, from about 0.05 go N to about 1.0 N may be resorted to. Also, while peptization is preferably eil'ected at elevated temperatures ranging from, say, 50 C. to about 90 *fi, efiective seeds may also be obtained by erely allowing the hydrate to stand in the g5 presence of cold hydrochloric acid at about 0.5

; N concentration. Siniildrly, while hydrochloric acid comprises a preferred type of peptizator, other agidic media, or mixtures thereof, may be Regent," being accordingly intended to embrace a drate from a solution of a soluble tin salt. fol

g peptizing or non-peptizing function. v Again, while the invention ha been illustrated '1};

sulfate solutions has been efie v 7 used, and particularly such other monobasic acids 5 i as nitric, perchloric, perbromic, periodic, hydro-' such conditioning agents as sulfuric acid, slycoilic acid, "5-, propionic acid, butyric acid, maleic acid, or salts,

bronuc, hydriodic; :-acetic. Additi,

a suspension of, colloidally dispersed, baptized, hydrous stannic oxide obtained by precipitating a stannic hydrate from a solution of a soluble tin.

monobasic acid medium at a concentration ranging from about 0.05. N. to about 1.0 N., and then maintaining the resulting mixture at a tempera,- ture of from about 50 C. to about 100 C. for a relatively short period of time to develop the nucleating characteristics oi said hydrous stannic oxide. a

2. A process for hydro a titanium sulfate solution to obtain aTiOa precipitate which converts to rutile on calcination at a temperature below substantially 1000 C. which comprises conducting hydrolysis thereof in the presence of a small amount of a nucleating agent comprising a suspension of colloidally dispersed, peptized, hydrous stannic oxide obtained by neutralizing an aqueous solution of a soluble tin salt to preat a concentration ranging from about 0.05 N. to

about 1.0 N., and thenmaintaining the resulting mixture at a temperature of from about 50 C.

suchfas sodium sulfate, aluminum sulfate, sodium cold sulfate, may also be used to produce the suspension or seed." The term conditioning all such useful types of acids or salts, whether inorganic or organic, and whether capable of tiin a preferred adaptation in which of a so render the same substantially free from electrostannic oxide nucleating sol may also be used in eiitecting hydrolysis of other solutions of titanium salts, such as the chloride, nitrate,-fluoride, characteristics of said hydrous stannic oxide, re- *'covering the precipitate obtained from said layhydrate may be obtained, said hydrate may be so "precipitated from other soluble salts of tin, and

through neutralization or otherwise, as irom aqfate, stannic fluoride, etc.

:ueous solutions of stannic bromida-pstannic sul- When said conditioned stannictoxicle em-1 'ployecl as a seeding agent in" the-hydrolysis of titanium salt solutions and the resultant T102 precipitate is subjected to oalcination at temperto about 100 C. for a relatively short period of time to develop the nucleating characteristics of said hydrous stannic oxide.

3. A process for producing a rutilevtitanium oxide pigment comprising hydrolyzing a titanium salt solution in the presence of a small amount of a nucleating agent comprising a suspension of colloidally dispersed, peptized, hydrous stannic oxide obtained by precipitating a stannic hylowed by washing of the resulting precipitate to lytes, after which said purified product is mixed with a monobasic acid peptizing agent at a concentration of about 0.05 N. to about 1.0 N., maintaining the resultin ure at a temperature of from about 50.to about 90 C. fora period of about 15-20 minutes to develop the nucleating titanium oxide pigment comprising hydrolyzing a titanium sulfate solution in the presence of from about 3 to about 5%, on the T1102 basis, of peptized stannic oxide prepared by precipitating a stannic hydrate through neutralization from a stores notexceeding substantially 850 6., the 1 pigment product obtained will consist of substan- "tially rutile titanium oxide of relativeiysmall funiiorm particle size average. In general, its as garage particle size will not exceed substantially 0.6 microns in diameter, and will yand soluble tin salt, washing the resulting precipitate,

to render the same substantially free from electrolytes, the resulting purified product with an cunt of hydrochloric acid suficient to provide a concentration of about 0.05 N. to about 1.0 N., mainta the resulting mixture at a temperature oi from about 50 to about 90 C. for

, preferably range from about 0.25 to below 0.l5

- microns.

In such state it will possess the highest titanium oxide hiding power value and requisite high tinting strength and color values as well.

- We claimas our invention:

p 1 Li. A process for hydrolyzing a titanium salt solution to obtain a TiO: precipitate which con- ;verts to rutile on calcination at a temperature be= "i low substantially 1000 C. which comprises conducting hydrolysis thereof in the presence of a about 15-20 utes to develop the nucleating characteristics of said stannic oxide, afterv hydrolysis of said titanium sulfate solution purifying and recovering the resulting anatase titanifuxn oxide hydrolysate, and then calcining the same at a temperature not exceeding substantially 850 C.

5. A process for obtaining an improved rutile titanium oxide pigment through conversion of anatase, at a temperature mlow substantially {all amount of anucleating agent compg 1000" 0., comprising hydrolyzing a titanium 8111..

sulting purified product with a monobasic acid peptizing agent at a concentration of about 0.05

N. to about 1.0 N., and then conditioning its nu- 1o cleating characteristics by maintaining said mixture for a relatively short period 0! time at a. temperature ranging from substantially 50-90 C., after hydrolysis of said titanium sulfate solution recovering and washing the anatase hydrolysate, and then calcining the same at a temperature not in excess of subtantially 850 C.

JOHN LEWIS KEATS. HENRY MORONI STARK. 

